Users of large amounts of electrical power such as cities, manufacturing facilities, and other high-power users are often located quite a distance away from sources of electrical power such as hydroelectric dams and power plants. In order to deliver large amounts of power from the source of generation to the power consumers, large, high-capacity, high-voltage power lines are used.
Typically, alternating current (“AC”) is generated in a three-phase configuration. For the purposes of this document, the three phases will be referred to as A, B and C phase. A phase, B phase and C phase are all transported over separate conductors. In some instances direct current (DC power) is used in which case two conductors are used and are referred to as A and C phase. Typically, the conductors are comprised of long wires supported on large support structures such as towers or power poles. The separate A, B and C phase conductors are typically attached to the same support structures on insulators.
From time to time, the power lines transporting the power may require maintenance. For example, a section of the conductor may need to be replaced, an insulator insulating the power line from the support structure may need to be replaced, or, the support structure itself may need repair or replacement. In some cases, conductors may be functioning properly, but need to be replaced by higher-capacity conductors in order to transport more power.
Typical maintenance on power lines requires that the power be shut off before the line can be worked on. High induction currents may be induced into a conductor located in the proximity of other high voltage conductors, thus creating a hazard in order to work on a particular conductor.
Shutting off the power creates a disruption of power delivery to customers. A power user may be forced to do without power during the time the power line is maintained, which is undesirable for a variety of reasons. To provide consumers power while a particular line is being worked on, the load may be shifted to other power lines to deliver the power to the end user. Unfortunately, shifting power to other transmission lines is not always possible because redundant systems may not exist, or transmission lines may already be operating at or near capacity level and not able to deliver the required power.
Previously, the applicant developed methods for conducting maintenance work on energized high voltage conductors in electrical transmission systems, such as the methods described in the U.S. Pat. No. 7,535,132 issued on May 19, 2009 to Quanta Associates, L.P. One of the methods taught in U.S. Pat. No. 7,535,132 involves moving each of the conductors needing replacement to a temporary position, stringing new conductors in or near the originating positions of the old conductors, transferring the power load from each of the old conductors to each of the new conductors using transfer buses, and removing the old conductors.
However, one problem that often occurs during the execution of the methods described in U.S. Pat. No. 7,535,132 is that the movement of each of the old conductors requiring replacement to temporary positions at the same time will often result in the transposition of the conductors carrying phases A, B and C, whereby, for example, if the phases were originally arranged in the relative horizontal positions of A-B-C prior to moving the phases to their temporary positions, the relative horizontal positions may often end up in the positions B-A-C after the movement has occurred. Furthermore, in order to achieve moving all three phases to temporary positions at the same time using the methods described in U.S. Pat. No. 7,535,132, it is often necessary to utilize long jumper cables to connect the temporarily relocated section of conductor to the remaining sections, which jumper cables for one phase must necessarily cross over the conductors of another phase while carrying a power load, as illustrated in FIG. 35 of U.S. Pat. No. 7,535,132. These are examples of what the Applicant refers to as illegal transpositions of the phase conductors. The disclosure of U.S. Pat. No. 7,535,132 is incorporated herein in its entirety, and is hereinafter referred to as the '132 patent.
Both scenarios described above results in the transposition of the phase conductors, leading to an imbalance in the impedances of the phase conductors and therefore, fluctuations in the voltage and current carried on the phase conductors. Such fluctuations, if large enough, will cause the protective relays to trip the breakers, causing a disruption in the delivery of power on the transmission lines being worked upon. To avoid this result, the owner of the power transmission line may choose to disable the safety relays while a live reconductoring project is underway. However, disabling the safety relays results in a risk that a sudden fluctuation in the voltage and current during the live reconductoring project may damage the transmission network.
Accordingly, it is desirable to provide an improved method to allow high voltage power transmission lines to be worked on, replaced or maintained without requiring power to stop being delivered or diverted over to other remote transmission lines, and without resulting in the illegal transposition of the phase conductors that could lead to faults in the transmission line.